Recording medium for hologram, hologram recording apparatus and hologram recording method

ABSTRACT

A recording medium ( 1 ) for hologram comprises a hologram recording layer ( 3 ) comprised of photo-polymer layer is formed on a base ( 2 ) comprised of colorless and transparent resin film, etc. and a protective layer ( 4 ) comprised of colorless and transparent resin film, etc. formed on the hologram recording layer ( 3 ). As such base ( 2 ) and protective layer ( 4 ), material having less double refraction is used. Optical axis of double refraction when such components are configured to be strip-shaped is allowed to be a direction of the longer side or a direction of the shorter side.

TECHNICAL FIELD

The present invention relates to a recording medium for hologram, andmore particularly to a recording medium for hologram of the type inwhich hologram recording layer comprised of photo-polymer layer isconfigured to be put between protective layer and base. Further, thepresent invention relates to a hologram recording apparatus and ahologram recording method for recording hologram onto a recording mediumfor hologram.

BACKGROUND ART

Holographic stereogram is prepared, e.g., by recording, in succession,onto single recording medium for hologram as strip-shaped or dot-shapedelement hologram, a large number of pictures, as original picture, whichare obtained by successively photographing object from different pointsof observation.

For example, in preparing holographic stereogram having parallaxinformation only in the lateral direction, such an approach is employedas shown in FIG. 1 to first photograph in succession object 100 fromdifferent points of observation in the lateral direction to therebyobtain parallax picture train 101 consisting of plural pictures havingparallax information in the lateral direction. It is to be noted that itis sufficient that such parallax picture train 101 is not pictureobtained by actually photographing object, but may be, e.g., CAD(Computer Aided Design) picture or CG (Computer Graphics) picturegenerated by computer etc. Further, respective pictures 102 constitutingthis parallax picture train 101 are recorded in succession onto arecording medium 103 for hologram as strip-shaped element hologram insuch a manner that they are successive in the lateral direction. Thus,holographic stereogram having parallax information in the lateraldirection can be obtained.

In this holographic stereogram, since information of plural pictures 102obtained by successively photographing object 100 from different pointsof observation in the lateral direction are recorded in succession insuch a manner that they are successive in the lateral direction asstrip-shaped element hologram, when observer looks at this holographicstereogram by the both eyes, two-dimensional picture images respectivelyimaged on his left and right eyes are different. Thus, the observerfeels parallax so that three-dimensional picture image is reproduced.

Meanwhile, element holograms of the above-mentioned holographicstereogram are recorded onto recording medium for hologram usingphotosensitive material as recording material in a manner stated below.Namely, in recording element holograms onto the recording medium forhologram, laser beams of good coherence are branched, and one branchedlaser beam is irradiated in a manner perpendicular to one surface of therecording medium for hologram as projected image (object light) whichhas been configured to undergo two-dimensional picture modulation bypicture display means, e.g., liquid crystal panel, etc. Further, theother branched laser beam is irradiated at a predetermined angle ontothe other surface of the recording medium for hologram as referencelight. Thus, interference patterns are formed as a change of refractiveindex or transmission factor at the photosensitive material of therecording medium for hologram so that element holograms are recorded.

As a recording medium for a hologram, there may be used, e.g., arecording medium of the type in which a hologram recording layerconsisting of photosensitive material such as photo-polymer, etc. isconfigured to be put between the protective layer and the base. Theobject light and the reference light are irradiated in the state oflinear polarization from one surface and the other surface of thehologram recording layer to form interference patterns to record elementholograms. It is to be noted that the photosensitive material of thehologram recording layer is not limited to photo-polymer, but there maybe used other photosensitive material, e.g., silver salt material orgelatin bichromate, etc.

As the protective layer and the base of such recording medium forhologram, the so-called optical material such as optically transparentresin or glass, etc. is used. Further, as such protective layer andbase, there is exemplified, e.g., transparent resin plate of such aspolycarbonate, polyolefin, PMMA (polymethyl methacrylate), etc. asdescribed in the Japanese Patent Publication No. H6-214117. Furthermore,there are exemplified PMMA (polymethyl methacrylate), polycarbonate,polyolefin, diethylene glycol bisallyl carbonate, polystyrene, hardpolyvinyl chloride, methylmethacrylate-styrene copolymer resin,styrene-acrylonitrile copolymer resin, and poly (4-methylpentene-1),etc., as described in the Japanese Patent Publication No. H10-119163.Further, Japanese Patent Publication No. 11-338336 discloses as examplessilicon compositions, etc. of condensation reactive type, additionreactive type, non-solvent type, ultraviolet hardening type and electronbeam hardening type, etc.

In addition, as structure of hologram recording medium includinghologram recording layer consisting of photo-polymer layer serving asphotosensitive material as described above, there are, as the structurealready announced, “Stephen A. Zager and Andrew M. Weber, “Displayholograms in Du Pont's Ommidex films”, Proc. of SPIE, Vol. 1461 (1991)pages 58–67 [DuPont]”, “T. J. Trout, W. J. Gambogi and S. H. Stevenson,“Photopolymer Materials for Color Holography”, Proc. SPIE, Vol. 2577(1995) pages 94–105”, “Sylvia H. Stevenson, “DuPont multicolorholographic recording films”, Proc. of SPIE, Vol. 3011 (1997)”, “MasamiKawabata, Akihiko Sato, Iwao Sumiyosi and Toshihiro Kubota,“Photopolymer system and its application to a color hologram” AppliedOptics, Vol. 33, No. 11 (Apr. 10, 1994) pages 2152–2156”, etc.

However, optical materials having small difference between refractiveindexes of double refraction are expensive. Further, according as doublerefraction becomes smaller or lesser, materials are limited, resultingin higher cost.

As described above, object light and reference light are incident on thehologram recording layer as linearly polarized light to forminterference patterns. However, when there is double refractioncharacteristic (birefringence) in the base or the protective layer,plane of polarization becomes oblique or changes into ellipticallypolarized light when such light is passed (transmitted) through the baseor the protective layer. For this reason, contrast of interferencepattern within the hologram recording layer is lowered.

As a method of solving such a phenomenon, there is mentioned a method ofreducing retardation which is one of index values of double refraction,i.e., reducing difference between refractive index in the direction inparallel to the optical axis and refractive index in the directionperpendicular to the optical axis as described in the Japanese PatentPublication No. H7-114329, for example.

However, optical materials having small difference between refractiveindexes of doble refraction are expensive.; Further, according as doublerefraction becomes smaller or lesser, materials are limited, resultingin higher cost.

In addition, in development and fixing of photosensitive material suchas silver salt material, gelatin bichromate, photo-polymer, etc. used inthe hologram recording layer, development process and fixing process arecarried out by acid/alkali, ultraviolet ray/visible ray/infrared ray,heat of high temperature or combination thereof, etc.

Under such circumstances, optical materials used in the protective layerand the base are also required to have various resistances ortolerances, e.g., chemicals resisting property such as acid resistanceor alkali resistance, etc., water proof property such as moisture proofproperty or swelling proof property, etc., light proof property such asyellowing proof property, etc., weathering resistance property such asheat resistance property or yellowing resistance property, etc.

Accordingly, optical materials having less double refraction andprovided with the above-mentioned resistances are limited and aretherefore very expensive.

DISCLOSURE OF THE INVENTION

The present invention has been proposed in view of actual circumstancesand is directed to a recording-medium for hologram in which projectedlight of a picture image and reference light are irradiated onto ahologram recording layer to thereby record the hologram, wherein a baseand a protective layer of the hologram recording layer comprise withmaterial having less double refraction.

Further, a hologram recording apparatus according to the presentinvention is directed to a hologram recording apparatus adapted forirradiating projected light of picture image and reference light onto ahologram recording layer to thereby record hologram, wherein axialdirection of double refraction of base and protective layer of thehologram recording layer is configured to be coincided with polarizationof the reference light and object light.

In addition, a hologram recording method according to the presentinvention is directed to a hologram recording method for irradiatingprojected light and reference light of a picture image onto a hologramrecording layer to thereby record hologram, wherein axial direction ofdouble refraction of a base and a protective layer of the hologramrecording layer coincides with polarized light of the reference lightand object light.

Still further objects of the present invention and more practical meritsobtained by the present invention will become more apparent from thedescription of the embodiments which will be given below.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view for explaining procedure-for making holographicstereogram.

FIG. 2 is a view for explaining photosensitive process ofphoto-polymerization type photo-polymer.

FIG. 3A is a view for explaining initial state in the photosensitiveprocess of photo-polymerization type photo-polymer.

FIG. 3B is a view for explaining exposure state in the photosensitiveprocess of photo-polymerization type photo-polymer.

FIG. 3C is a view for explaining fixing state in the photosensitiveprocess of photo-polymerization type photo-polymer.

FIG. 4 is a view for explaining the state where one laser beam isincident on recording medium for hologram composed of base and hologrammrecording layer through polarization plate.

FIG. 5 is a view for explaining the state where reference light andobject light are respectively incident on recording medium for hologramcomposed of base, hologram recording layer and protective layer throughpolarization plates.

FIG. 6A is a view for explaining optical state of materials of base andprotective layer constituting recording medium for hologram by usingrefractive index elliptical body, wherein axial direction of doublerefraction is configured to be coincided with thickness direction of therecording medium for hologram.

FIG. 6B is a view for explaining optical state of materials of base andprotective layer constituting recording medium for hologram by usingrefractive index elliptical body, wherein axial direction of doublerefraction is configured to be coincided with a direction of the longerside of the recording medium for hologram.

FIG. 6C is a view for explaining optical state of materials-of base andprotective layer constituting recording medium for hologram by usingrefractive index elliptical body, wherein axial direction of doublerefraction is configured to be coincided with a direction of the shorterside of the recording medium for hologram.

FIG. 7 is a view showing the configuration of a holographic stereogrampreparing apparatus.

FIG. 8A is a view for explaining the configuration of exposureprocessing unit in the above-mentioned holographic stereogram preparingapparatus, wherein the entire optical system is viewed from the upwarddirection.

FIG. 8B is a view for explaining the configuration of exposureprocessing unit in the above-mentioned holographic stereogram preparingapparatus, wherein the portion for object light of the optical system isviewed from lateral direction.

FIG. 9 is a view for explaining detailed configuration of printer headportion in the above-mentioned holographic stereogram preparingapparatus.

FIGS. 10A and 10B are views for explaining states of double refractionin the case where laser beams are obliquely incident and in the casewhere laser beams are perpendicularly incident.

FIG. 11 is a cross sectional view of recording medium for hologram offive layer structure comprising two hologram recording layers.

FIG. 12 is a cross sectional view of recording medium for hologram ofseven layer structure comprising three hologram recording layers.

BEST MODE FOR CARRYING OUT THE INVENTION

Preferred embodiments of the present invention will now be describedwith reference to the attached drawings. It should be noted that thepresent invention is not limited to the following examples, and it istherefore needless to say that modification/change may be made withinthe range which does not depart from the gist of the present invention.

Initially, explanation will be given with reference to FIG. 2 inconnection with a more practical example of a recording medium forhologram. This recording medium 1 for hologram is adapted so that ahologram recording layer 3 comprised of photo-polymer layer is formed ona base 2 comprised of colorless and transparent resin film, etc. and aprotective layer 4 comprised of colorless and transparent resin film,etc. is formed on the hologram recording layer 3. Thicknesses of thebase 2 and the protective layer 4 and intermediate layer which will bedescribed later are 5 μm to 100 μm, and thickness of the hologramrecording layer 3 is 20 μm.

It is preferable that there is used for the hologram recording layer 3photo-polymer configured to be of film structure, which is suitable forrecording interference patterns taking place by interference betweenreference light and object light as change of refractive index. In thephoto-polymer configured to be of film structure, by irradiating light,refractive index of material is changed. In this embodiment, as thehologram recording layer 3, there is used, e.g., photopolymerizationtype photo-polymer such as “OMNI-DEX” (Trade Name) by DuPont Company,etc. In the photopolymerization type photo-polymer, in the initialstate, as shown in FIG. 3A, monomers Mare uniformly dispersed withinmatrix polymer. Oh the contrary, when light La of power of about 10 to400 mJ/cm² is irradiated as shown in FIG. 3B, monomers M of the exposedportions are polymerized in dependency upon power of irradiated lightLa. As a result, densities of monomers locally change so that refractiveindex modulation takes place. Thereafter, by irradiating ultravioletrays Lb of power of about 1000 mJ/cm² onto the entire surface as shownin FIG. 3C, polymerization of monomers M is completed. Thus, refractiveindex modulation degree is enhanced and the refractive index modulationis fixed.

Meanwhile, in recording three-dimensional picture onto hologramrecording layer 3 comprised of the above-mentioned photo-polymerizationtype photo-polymer, as described later, reference light is transmittedthrough the base 2 so that it is incident on the hologram recordinglayer 3, and object light is transmitted through the protective layer 4so that it is incident on the hologram recording layer 3. Thus, suchinterference patterns are recorded onto the hologram recording layer 3.Accordingly, the base 2 and the protective layer 4 are required to haveoptical characteristics such as less double refraction, less lightscattering and high light transmission factor, etc. Particularly, sincewhen rays of linearly polarized light of object light and referencelight are transmitted through the base 2 and the protective layer 4,plane of polarization becomes oblique or they change into rays ofelliptical polarized light different from each other in dependency upondouble refraction of the base 2 and the protective layer 4, there is thepossibility that contrast of interference pattern within the hologramrecording layer 3 may be lowered.

How double refraction of the base 2 or double refraction of theprotective layer 4 affects contrast of interference pattern formed atthe hologram recording layer 3 will be described below in detail.

First, how polarization state changes in the case where laser beamshaving linearly polarized light are incident on the hologram recordinglayer through the base or the protective layer having double refractionwill be explained.

The state where one laser beam L is incident, through a polarizationplate 50, on a recording medium 51 for hologram composed of a hologramrecording layer 53 provided at one side and a base 52 provided at theother side as shown in FIG. 4 is assumed as simple model.

Laser beam L is incident on the recording medium 51 for hologram throughthe polarization plate 50 and is transmitted through the base 52 havingdouble refraction so that there takes place change in the polarizationstate. Thereafter, such laser beam is incident on the hologram recordinglayer 53. It is here to be noted that while laser beam L is assumed tobe incident on the recording medium 51 for hologram through thepolarization plate 50, such explanation is given for the purpose offacilitating that laser beam L is linearly polarized in the x-direction,and it is assumed that there is no absorption by the polarization plate50.

Here, it is assumed-that the wavelength of laser beams is λ, electricfield vector of laser beams in the state linearly polarized in thex-direction is Ē^(in), and thickness of base-having double refraction isd. Here, for the brevity, the optical axis of the base having doublerefraction is assumed to be within the xy plane, refractive index in theaxial direction is assumed to be n_(e), refractive index in-thedirection perpendicular thereto is assumed to be n_(o), and direction ofthe axis is assumed to form angle φ in the x-direction.

Further, unit vectors in x, y and z directions are respectively assumedto be ē_(x), ē_(y), ē_(z), and unit vectors in the axis direction ofdouble refraction and in the direction perpendicular thereto arerespectively assumed to be ē_(e), ē_(o). At this time, with respect tothese unit vectors, the relationship indicated by the following formula(1) holds.

$\begin{matrix}\left\{ {\begin{matrix}{{\overset{\_}{e}}_{e} = {{\cos\;{\phi \cdot {\overset{\_}{e}}_{x}}} + {\sin\;{\phi\; \cdot {\overset{\_}{e}}_{y}}}}} \\{{\overset{\_}{e}}_{o} = {{\sin\;{\phi \cdot {\overset{\_}{e}}_{x}}} - {\cos\;{\phi \cdot {\overset{\_}{e}}_{y}}}}}\end{matrix}\left\{ \begin{matrix}{{\overset{\_}{e}}_{x} = {{\cos\;{\phi \cdot {\overset{\_}{e}}_{e}}} + {\sin\;{\phi\; \cdot {\overset{\_}{e}}_{o}}}}} \\{{\overset{\_}{e}}_{y} = {{\sin\;{\phi \cdot {\overset{\_}{e}}_{e}}} - {\cos\;{\phi \cdot {\overset{\_}{e}}_{o}}}}}\end{matrix} \right.} \right. & (1)\end{matrix}$

In this model, the electric field-vector of the incident laser beams Lis expressed as E^(in)=E^(in) e_(x) by using complex amplitude E^(in)and laser beams L in the state linearly polarized in the x-direction isassumed to be incident on the base 52 having double refraction. Whenelectric field vector before laser beams are—incident is separated intotwo components Ē_(e) ^(in), Ē_(o) ^(in)—the direction of the axis ofdouble refraction and in the direction perpendicular thereto, it isexpressed as the following formula (2)

$\begin{matrix}{{\overset{\_}{E} = {{{\overset{\_}{E}}_{e}^{in} + {\overset{\_}{E}}_{o}^{in}} = {{E^{in}{\overset{\_}{e}}_{x}} = {{E^{in}\cos\;{\phi \cdot {\overset{\_}{e}}_{e}}} + {E^{in}\sin\;{\phi\; \cdot {\overset{\_}{e}}_{o}}}}}}}\left\{ \begin{matrix}{{\overset{\_}{E}}_{e}^{in} = {{E^{in}\cos^{2}\;{\phi \cdot {\overset{\_}{e}}_{x}}} + {E^{in}\cos\;\phi\;\sin\;{\phi \cdot {\overset{\_}{e}}_{y}}}}} \\{{\overset{\_}{E}}_{o}^{in} = {{E^{in}\sin^{2}\;{\phi \cdot {\overset{\_}{e}}_{x}}} - {E^{in}\sin\;\phi\;\cos\;{\phi\; \cdot {\overset{\_}{e}}_{y}}}}}\end{matrix} \right.} & (2)\end{matrix}$

These electric field vectors of two components are passed through thebase 52 having double refraction, thereby they respectively undergophase changes of 2πin_(e)d/λ and 2πin_(o)d/λ. Thus, electric fieldvector Ē^(out) out passed/emitted through the base 52 and incident onthe hologram recording layer 53 is expressed as the following formulas(3), (4) in the state separated into two components Ē_(e) ^(out), Ē_(o)^(out) in the direction of the axis and in the direction perpendicularthereto.

$\begin{matrix}\begin{matrix}{{\overset{\_}{E}}_{e}^{out} = {{\overset{\_}{E}}_{e}^{in} \cdot {\exp\left( {2\pi\; i\; n_{e}{d/\lambda}} \right)}}} \\{= {{{\overset{\_}{E}}^{in}\cos^{2}{\phi \cdot {\exp\left( {2\;\pi\; i\; n_{e}{d/\lambda}} \right)} \cdot {\overset{\_}{e}}_{x}}} + {{\overset{\_}{E}}^{in}\cos\;\phi\;\sin\;{\phi \cdot {\exp\left( {2\;\pi\; i\; n_{e}{d/\lambda}} \right)} \cdot {\overset{\_}{e}}_{y}}}}}\end{matrix} & (3) \\\begin{matrix}{{\overset{\_}{E}}^{out} = {{\overset{\_}{E}}_{o}^{in} \cdot {\exp\left( {2\pi\; i\; n_{o}{d/\lambda}} \right)}}} \\{= {{E^{in}\sin^{2}{\phi \cdot {\exp\left( {2\;\pi\; i\; n_{o}{d/\lambda}} \right)} \cdot {\overset{\_}{e}}_{x}}} - {E^{in}\sin\;\phi\;\cos\;{\phi \cdot {\exp\left( {2\;\pi\; i\; n_{o}{d/\lambda}} \right)} \cdot {\overset{\_}{e}}_{y}}}}}\end{matrix} & (4)\end{matrix}$

Thus, electric field vector E^(out) is expressed as the followingformula (5).

$\begin{matrix}\begin{matrix}{{\overset{\_}{E}}^{out} = {{\overset{\_}{E}}_{e}^{out} + {\overset{\_}{E}}_{o}^{out}}} \\{= {E^{in}{\left\{ {{\cos^{2} \cdot \phi \cdot {\exp\left( {2\;\pi\; i\; n_{e}{d/\lambda}} \right)}} + {\sin^{2}{\phi \cdot {\exp\left( {2\;\pi\; i\; n_{o}{d/\lambda}} \right)}}}} \right\} \cdot}}} \\{{~~}{{\overset{\_}{e}}_{x} + \;{E^{in}\cos\;\phi\;\sin\;{\phi \cdot \left\{ {{\exp\left( {2\;\pi\; i\; n_{e}{d/\lambda}} \right)} - {\exp\left( {2\;\pi\; i\; n_{o}{d/\lambda}} \right)}} \right\} \cdot {\overset{\_}{e}}_{y}}}}}\end{matrix} & (5)\end{matrix}$

From this formula, it is seen that when φ=0[rad], φ=π/2[rad] orn_(e)=n_(o) does not hold by the effect of double refraction, the e_(y)component takes place in electric field vector E^(out) incident on thehologram recording layer 53, thus the changes of polarization statetaking place, which change is, for example, the rotation of plane ofpolarization with respect to incident light, etc.

It is to be noted that it has been explained for simplification thatoptical axis of base having double refraction is within the xy plane.However, similar explanation can be given to the case where the opticalaxis of the base having double refraction is not within the xy planewhile replacing two refractive indexes n₁, n₂ which form long axis andshort axis of ellipse indicating refractive index by n_(e), no, in viewof the relationship between propagation direction of rays (pointingvector) and refractive index vector plane, i.e., in view of therelationship indicated by ellipse prepared by plane perpendicular towave vector and refractive index, elliptical body from an intuitivepoint of view.

Secondly, an explanation will be given-in connection with the casewhere, for recording of hologram, two laser light fluxes having linearpolarization are passed through the base or the protective layer havingdouble refraction so that they are incident on the hologram recordinglayer and-interfere with each other.

There is assumed two light flux interference model that, as shown inFIG. 5, reference light L4 is transmitted through the base 2 and isincident on the hologram recording layer 3 with respect to the recordingmedium 1 for hologram composed of base 2, hologram recording layer 3 andprotective layer 4, and object light L3 is transmitted through theprotective layer 4 and is incident on the hologram recording layer 3,whereby interference patterns thereof are formed on the hologramrecording layer 3.

Reference light L4 is incident on the recording medium 1 for hologramthrough a polarization plate 60, and is transmitted through the base 2having double refraction so that there takes place change in thepolarization state. Thereafter, this reference light L4 is incident onthe hologram recording layer 3. On the other hand, object light L3 isalso incident on the recording medium 1 for hologram through apolarization plate 61, and is transmitted through the protective layer 4having double refraction so that there takes place change in thepolarization state. Thereafter, this object light is incident on thehologram recording layer 3. It is to be noted that reference light L4and object light L3, are assumed to be incident on the recording medium1 for hologram through polarization plates 60, 61, such assumption ismade in order to easily understand that laser beams are linearlypolarized in the x-direction and it is assumed that there is noabsorption by the polarization plate.

Here, wavelength of laser beams of reference light L4 and object lightL3 is assumed to be λ. With respect to the reference light LA side,electric field vector of reference light in the state linearly polarizedin the x-direction is assumed to be E^(ref,in) and thickness of base 2having double refraction is assumed to be d^(ref). It is here to benoted for simplification that optical axis of base 2 having doublerefraction is assumed to be within the xy plane, refractive index in theaxial direction is assumed to be n_(e) ^(ref), refractive index in thedirection perpendicular thereto is assumed to be n_(o) ^(ref), anddirection of the axis is assumed to form angle φ in the x-direction.With respect to the object light L3 side, electric field vector ofobject light L3 in the state linearly polarized in the x-direction isassumed to be Ē^(obj,in) and thickness of the protective layer 4 havingdouble refraction is assumed to be d^(obj). Here, for simplification,the optical axis of the protective layer 4 having double refraction isassumed to be within xy-plane, refractive index in the axial directionis assumed to be n_(o) ^(obj), refractive index in the-directionperpendicular thereto is assumed to be n_(o) ^(obj) and direction of theaxis is assumed to form angle ψ in the x-direction.

In this model, electric field vector of incident reference light L4 isassumed to be expressed as Ē^(ref,in)=E^(ref,in) ē_(x) by using complexamplitude E^(ref,in), and reference light in the state linearlypolarized in the x-direction is assumed to be incident on the base 2having double refraction. In addition, electric field vector of incidentobject light L3 is assumed to be expressed as Ē^(obj,in)=E^(obj,in)ē_(x) by using complex amplitude E^(obj,in) and object light L3 in thestate linearly polarized in the x-direction is assumed to be incident onthe protective layer 4 having double refraction.

From the result obtained by the model shown in FIG. 4, electric fieldvector Ē^(ref,out) of reference L4 passed/emitted through the base 2 andincident on the hologram recording layer 3 is represented by thefollowing formula (6).

$\begin{matrix}\begin{matrix}{{\overset{\_}{E}}^{{ref},{out}} = {{\overset{\_}{E}}^{{ref},{out}} + {\overset{\_}{E}}_{o}^{{ref},{out}}}} \\{= {E^{{ref},{in}}\left\{ {{\cos^{2}{\phi \cdot {\exp\left( {2\;\pi\; i\; n_{o}^{ref}{d^{ref}/\lambda}} \right)}}} +} \right.}} \\{{{\left. {\sin^{2}{\phi \cdot {\exp\left( {2\;\pi\; i\; n_{o}^{ref}{d^{ref}/\lambda}} \right)}}} \right\}} \cdot {\overset{\_}{e}}_{x}} +} \\{E^{{ref},{i\; n}}\cos\;\phi\mspace{14mu}\sin\;{\phi \cdot \left\{ {{\exp\left( {2\;\pi\; i\; n_{e}^{ref}{d^{ref}/\lambda}} \right)} -} \right.}} \\{{\left. {\exp\left( {2\pi\; i\; n_{o}^{ref}{d^{ref}/\lambda}} \right)} \right\}} \cdot {\overset{\_}{e}}_{y}}\end{matrix} & (6)\end{matrix}$

Moreover, the electric field vector Ē^(obj,out) of the object light L3passed/emitted through the protective layer 4 and incident on thehologram recording layer 3 is represented by the following formula (7).

$\begin{matrix}\begin{matrix}{{\overset{\_}{E}}^{{obj},{out}} = {{\overset{\_}{E}}_{e}^{{obj},{out}} + {\overset{\_}{E}}_{o}^{{obj},{out}}}} \\{= {E^{{obj},\;{i\; n}}\left\{ {{\cos^{2}{\varphi \cdot {\exp\left( {2\;\pi\; i\; n_{e}^{obj}{d^{obj}/\lambda}} \right)}}} +} \right.}} \\{{\left. {\sin^{2}{\varphi \cdot {\exp\left( {2\;\pi\; i\; n_{o}^{obj}{d^{obj}/\lambda}} \right)}}} \right\} \cdot {\overset{\_}{e}}_{x}} +} \\{E^{{obj},{i\; n}}\cos\;\varphi\mspace{14mu}\sin\;{\varphi \cdot \left\{ {{\exp\left( {2\;\pi\; i\; n_{e}^{obj}{d^{obj}/\lambda}} \right)} -} \right.}} \\{{\left. {\exp\left( {2\pi\; i\; n_{o}^{obj}{d^{obj}/\lambda}} \right)} \right\}} \cdot {\overset{\_}{e}}_{y}}\end{matrix} & (7)\end{matrix}$

As a result, the light intensity I of interference patterns which can beformed on the hologram recording layer 3 is a square of absolute valueof sum of the electric field vectors of the reference light L4 and theobject light L3, and is represented by the following formula (8) whenphase change values taking place as the result of the fact that rays ofsuch light are passed through the base 2 and the protective layer 4having double refraction are respectively indicated by N_(e) ^(ref),N_(o) ^(ref), N_(e) ^(obj), N_(o) ^(obj).

$\begin{matrix}\begin{matrix}{I = {{{\overset{\_}{E}}^{{ref},{out}} + {\overset{\_}{E}}^{{obj},{out}}}}^{2}} \\\left. = \middle| \left\lbrack {{E^{{ref},\;{i\; n}}\left\{ {{\cos^{2}{\phi \cdot N_{e}^{ref}}} + {\sin^{2}{\phi \cdot N_{o}^{ref}}}} \right\}} + {{\overset{\_}{E}}^{{obj},{i\; n}}\left\{ {{\cos^{2}{\varphi \cdot N_{e}^{obj}}} +} \right.}} \right. \right. \\{{\left. \left. {\sin^{2}{\varphi \cdot N_{o}^{obj}}} \right\} \right\rbrack \cdot {\overset{\_}{e}}_{x}} +} \\{\left\lbrack {{E^{{ref},\;{i\; n}}\cos\;{\phi \cdot \sin}\;{\phi \cdot \left\{ {N_{e}^{ref} - N_{o}^{ref}} \right\}}} + {{\overset{\_}{E}}^{{obj},\;{i\; n}}\cos\;\varphi\mspace{11mu}\sin\;{\varphi \cdot}}} \right.} \\\left. {{\left. \left\{ {N_{e}^{obj} - N_{0}^{obj}} \right\} \right\rbrack} \cdot {\overset{\_}{e}}_{y}} \right|^{2} \\{= {{{E^{{ref},\;{i\; n}}\left\{ {{\cos^{2}{\phi \cdot N_{e}^{ref}}} + {\sin^{2}{\phi \cdot N_{o}^{ref}}}} \right\}} + {{\overset{\_}{E}}^{{obj},{i\; n}}\left\{ {{\cos^{2}{\varphi \cdot N_{e}^{obj}}} +} \right.}}}} \\\left. \left. {\sin^{2}\varphi\; N_{o}^{obj}} \right\} \middle| {}_{2} + \right. \\{\left| {{E^{{ref},\;{i\; n}}\cos\;\phi\mspace{14mu}\sin\;{\phi \cdot \left\{ {N_{e}^{ref} - N_{0}^{ref}} \right\}}} +} \right.} \\{\left. {E^{{obj},{i\; n}}\cos\mspace{11mu}\varphi\mspace{11mu}\sin\;\varphi\left\{ {N_{e}^{obj} - N_{o}^{obj}} \right\}} \right|^{2}}\end{matrix} & (8)\end{matrix}$

Here, the phase changes N_(e) ^(ref), N_(o) ^(ref), N_(e) ^(obj), N_(o)^(obj) are represented by the following formula (9).N _(e) ^(ref) =exp(2πin _(e) ^(ref) d ^(ref)/λ), N _(o) ^(ref) =exp(2πin_(o) ^(ref) d ^(ref)/λ) N _(o) ^(obj) =exp(2πin _(o) ^(obj) d ^(obj)/λ),N _(o) ^(obj) =exp(2πin _(o) ^(obj) d ^(obj)/λ)  (9)

From the formula of light intensity I of this interference pattern, inthe case where a certain reference light L4 and a certain object lightL3 which are respectively perpendicularly incident on the recordingmedium 1 for hologram are given, in order to maximize contrast of lightintensity of interference pattern, polarization states of referencelight L4 and object light L3 are configured to be the same, i.e.,relationship therebetween is configured to be represented by thefollowing formula (10).|E ^(ref,in)cosφsinφ·{N _(e) ^(ref) −N _(o) ^(ref) }|=|E^(obj,in)cosφsinφ·{N _(e) ^(obj) −N _(o) ^(obj)}|  (10)

Here, for simplification, even in the case where light intensities ofreference light L4 and object light L3 are equal to each other (i.e.,absolute values of complex amplitudes of the reference light and theobject light are equal to each other), namely,|E^(ref,in)|=|E^(obj,in)|1, it is necessary to satisfy the followingformula (11).cosφsinφ·|exp(2πin _(o) ^(ref) d ^(ref)/λ)−exp(2πin _(o) ^(ref) d^(ref)/λ)|=cosφsinφ·|exp(2πin _(o) ^(obj) d ^(obj)/λ)−exp(2πin _(o)^(obj) d ^(obj)/λ)|  (11)

As the result of the above, in order to satisfy this formula (11), suchan approach is employed that, with respect to material of the base 2,thickness is configured to be d^(ref), refractive index in the axialdirection of double refraction of the base is configured to be n_(e)^(ref), refractive index in the direction perpendicular thereto isconfigured to be n_(o) ^(ref) and direction of the axis is configured toform angle φ in the x-direction, and, with respect to material of theprotective layer 4, thickness is configured to be d^(obj), refractiveindex in the axial direction of double refraction of the protectivelayer 4 is configured to be n_(e) ^(obj), refractive index in thedirection perpendicular thereto is configured to be n_(o) ^(obj), andaxial direction is configured to form angle ψ in the x-direction. Thus,recording of hologram of good contrast of interference pattern which canbe formed at the hologram recording layer 3, i.e., high diffractionefficiency can be made.

As the solution of the above-mentioned formula (11), plural solutionsare given by the above-mentioned eight values, i.e., d^(ref), n_(e)^(ref), n_(o) ^(ref), φ, d^(obj), n_(e) ^(obj), n_(o) ^(obj), ψ.Particularly, when (a) in the base, n_(e) ^(ref)=n_(o) ^(ref), φ=0[rad]or φ=π/2[rad] is configured to hold, (b) in the protective layer, n_(e)^(obj)=n_(o) ^(obj), ψ=0[rad] or ψ=π/2[rad] is configured to hold,satisfying of (a) and (b) at the same time constitutes one of solutions.

To put it in physical expression, satisfying of both phrases of (a), inthe base, “there is no double refraction in the base” with respect toincident direction of reference light, “direction of linear polarizationof reference light is the same as axial direction of double refractionof base” or “direction of linear polarization of reference light is thesame as direction perpendicular to the axis of double refraction of thebase”, and (b), in the protective layer, “there is no double refractionin the protective layer” with respect to incident direction of objectlight, “direction of linear polarization of object light is the same asaxial direction of double refraction of the protective layer”, or“direction of linear polarization of object light is the same asdirection perpendicular to the axis of double refraction of theprotective layer” constitutes one of solutions.

The relationship between these (a) and (b) results in the relationshipbetween irradiation states of reference light and object light and therecording medium for hologram, and relates to a making method or arecording apparatus for holographic stereogram or hologram.

On the contrary, geometrical shape of the recording medium for hologramand axial direction of double refraction of the base and the protectivelayer constituting the recording medium for hologram are configured tohave relationship similar to (a) and (b), thereby making it possible tounify, every apparatuses, polarization states of recording apparatusesfor holographic stereogram or hologram.

Namely, with respect to geometrical shape of the strip-shaped or thelike recording medium for hologram having the longer side and theshorter side, axial direction of double refraction of optical materialconstituting the recording medium for hologram is configured to becoincided with the longer side or the shorter side, or the directionperpendicular to the axis of double refraction is configured to becoincided with the longer side or the shorter side.

When optical state of material of base 2 and protective layer 4constituting such a recording medium 1 for hologram is illustrated byusing refractive index elliptical body, there results optical state asshown in FIG. 6. This FIG. 6 shows the example where uniaxial opticalmaterial is used.

In FIG. 6A, axial direction Y of double refraction of uniaxial opticalmaterial is configured to be coincided with thickness direction of astrip-shaped recording medium 65 for hologram. By doing so, thereresults the state where there is no double refraction with respect tolaser beams L incident in a manner perpendicular to recording medium 65for hologram.

In FIG. 6B, axial direction Y of double refraction of uniaxial opticalmaterial is configured to be coincided with a direction of the longerside of strip-shaped recording medium 66 for hologram. Thereby, it iseasy that there results the state where direction of linear polarizationis configured to be the same as axial direction of double refraction orthe state perpendicular thereto with respect to laser beams L incidenton recording medium 66 for hologram.

In FIG. 6C, the axial direction Y of double refraction of uniaxialoptical material is configured to be coincided with a direction of theshorter side of strip-shaped recording medium 67 for hologram. Thereby,it is easy that there results the state where direction of linearpolarization is configured to be the same as axial direction of doublerefraction or the state perpendicular thereto with respect to laserbeams L incident on recording medium 67 for hologram.

By the above-described invention, it is possible to univocally determinepolarization state of the hologram recording apparatus in a mannercoincided with geometrical shape of the strip-shaped recording mediumfor hologram as in the above-mentioned example shown. On the contrary,such an approach is employed to unify and standardize polarizationstates of hologram recording apparatuses every apparatuses, therebymaking it possible to unify and standardize geometrical shape of therecording medium for hologram. Thus, in both the hologram recordingapparatus and the recording medium for hologram, mass production can bemade and reduction in cost can be realized.

Namely, as the base 2 and the protective layer 4, there is used materialin which axial direction of double refraction is configured to becoincided with geometrical shape of the recording medium for hologram,and is desirably used material of less double refraction, andinterference patterns of three-dimensional image are recorded onto thehologram recording layer 3. Thus, recording of interference patterns ofgood contrast can be carried out. Furthermore, by irradiatingreproduction light onto those interference patterns, reproduction ofhigh diffraction efficiency can be made, and reproduction image is ofhigh quality. From this fact, it can be said that there holds apredetermined relationship with respect to quality of reproductionimage, diffraction efficiency and quantity and state of doublerefraction.

Let suppose the case where polymer material (resin material) is used inthe state of film (thin film structure) as optical materials used forthe protective layer and the base.

Even in the case where raw material having less double refraction isused as optical material, there are instances where double refractiontakes place at the time of molding. Particularly, in the case wherematerial is configured to be of film structure for the purpose of usingit as the base, the protective layer or the intermediate layer of therecording medium for hologram, since expansion process is added for thepurpose of molding, double refraction is easy to take place. This isbecause shape of refractive index elliptical body mainly depends uponpolarization state of molecular ring in polymer material. Namely,optical axis of double refraction greatly depends upon polarizationfactor and bonding direction of molecule.

Thus, in the case of allowing polymer material to be of film structure,although depending upon components of raw material used, quantity ofdouble refraction becomes greatly different depending upon itsmanufacturing method. In particular, in expanding process, which istypical manufacturing method for film, there are many instances wheremolecular ring is expanded in expanding direction and double refractionwhich was less in the row material is also increased depending uponexpanding state.

Thus, the recording medium for hologram is used in the state where axialdirection of double refraction is configured to be coincided withgeometrical shape thereof as in this embodiment, thereby making itpossible to use such inexpensive material typically manufactured asoptical film.

In addition to the above, it is more desirable to use material havingless double refraction as raw material. As material having less doublerefraction, there can be used, e.g., material obtained by allowingtransparent resin (optical plastic, optical polymer) developed as basematerial for optical disc to be of film structure. In the structure ofthe above-described and already announced recording medium for hologram,polyethylene terephthalate (PET), and vinyl chloride (PVC) are used, butsuch materials are not suitable from viewpoints of double refraction andtransparency. As the material, material called non-double refractiveoptical polymer is desirable.

When desirable materials are exemplified, there is polycarbonate resin(PC). As material having double refraction lesser than that, there ismethacrylic resin (acryl, PMMA). As material having double refractionlesser than methacrylic resin, there are “ZEONEX” (Trade Name, NipponZeon Co., Ltd.), “ARTON” (Trade Name, JSR Kabushiki Kaisha), “APEL”(Trade Name, Mitsui Kagaku Kabushiki Kaisha) and “Olefin MaleimideCopolymer” (Tosoh Kabushiki Kaisha) which are classified into alicyclicolefin (amorphous polyolefin). As other material having less doublerefraction, there is “Optolez” (Trade Name, Product Names OZ-1000,OZ-1100, OZ-1310, OZ-1330, etc., Hitachi Kasei Kogyo Kabushiki Kaisha)which is classified into alicydlic acryl.

In addition to the above, it is further desirable to use material suchthat double refraction is difficult to take place with respect toexpansion. As one method thereof, there is used material manufactured bymethod of random-copolymerizing monomer indicating inverse (plus orminus) double refraction characteristic with the above-mentionedpolymer. In particular, it is desirable to use, as the base, theprotective layer and the intermediate layer of the recording medium forhologram, film by material in which stilbene is 3% doped by weight inPMMA as indicated in “Iwata et al. Proceedings of Polymer Society,V61.45, No. 3 page 461 (1996)”.

Three-dimensional picture is recorded, as holographic stereogram, ontothe recording medium 1 for hologram in which hologram recording layer 3is configured to be put between the above-described base 2, protectivelayer 4 and/or intermediate layer which will be described later, whichconsist of materials as described above.

Subsequently, holographic stereogram preparing apparatus for recordingthree-dimensional picture onto the above-described recording medium 1for hologram as holographic stereogram will be described. Whileexplanation will be given here in connection with the apparatus forrecording strip-shaped plural element holograms onto one recordingmedium 1 for hologram to thereby prepare holographic stereogramconfigured to have parallax information in the lateral direction and-inthe longitudinal direction, there may be also mentioned, e.g., anapparatus for recording dot-shaped element hologram onto one recordingmedium 1 for-hologram to thereby prepare L holographic stereogramconfigured to have parallax information in the lateral direction and inthe longitudinal direction.

This holographic stereogram preparing apparatus is directed to a makingapparatus for the so-called one step holographic stereogram, and isadapted to output, as holographic stereogram, recording medium 1 itselfwhere interference pattern between object light and reference light arerecorded.

As shown in FIG. 7, this holographic stereogram preparing apparatus(unit) is composed of a data processing unit 21 for carrying outprocessing of picture data to be recorded, a computer 22 for controlwhich carries out control of the-entirety of this system, and anexposure processing unit 23 including an optical system for makingholographic stereogram.

The data processing unit 21 reads thereinto parallax picture train D1from parallax picture train imaging section or parallax picture traingeneration computer, etc. to implement predetermined picture processingfor holographic stereogram, e.g., view point conversion processingand/or keystone distortion correction processing, etc. to the parallaxpicture train D1 by a picture processing computer 24 to store (record)picture data D2 to which-predetermined processing has been implementedinto a memory section 25 such as memory or hard disc, etc.

In this example, the parallax picture train imaging section delivers, tothe picture processing computer 24, as parallax picture train D1, e.g.,picture image obtained by photographing object from different pluralview points in lateral direction by simultaneous photographing bymulti-eye type camera or successive photographing by movement typecamera, etc.

Furthermore, the parallax picture train generation computer preparesparallax picture train D1 consisting of plural picture images includingparallax information by making use of the technique such as CAD or CG,etc. to deliver this parallax picture train D1 to the picture processingcomputer 24.

Furthermore, the data processing unit 21 reads out, in order, picturedata every one picture from the memory section 25 when preparingholographic stereogram to send out this picture data D3 to the controlcomputer 22.

The control computer 22 controls the exposure processing unit 23 torecord, in succession, as strip-shaped element holograms, picture imagesbased on picture data D3 delivered from the data processing unit 21 ontothe recording medium 1 for hologram set within the exposure processingunit 23.

At this time, the control computer 22 carries out control of shutter,display section and printer head portion, etc provided at the exposureprocessing unit 23 as described later. Namely, the control computer 22sends out a control signal S1 to the shutter to control opening/closingoperations of the shutter, delivers picture data D4 to the displaysection to allow the display section to display picture image based onthe picture data D4, and sends out a control signal S2 to the printerhead portion to control sending operation, etc. of the recording medium1 for hologram by the printer head portion.

Subsequently, the exposure processing unit 23 will be described indetail with reference to the attached drawings. Here, FIG. 8A is a viewin which the optical system of the entirety of the exposure processingunit 23 is viewed from the upper direction and FIG. 8B is a view inwhich the portion for object, light of the optical system of theexposure processing unit 23 is viewed from lateral direction. It is tobe noted that the optical system is not required to have configurationas shown in FIG. 8A and FIG. 8B, but if there is employed such aconfiguration capable of preparing holographic stereogram, e.g.,incident direction of reference light, the number of lenses, the kindthereof and combination thereof may be suitably changed.

As shown in FIG. 8A, the exposure processing unit 23 comprises a laserlight source 31 for emitting laser beams of a predetermined wavelength,and a shutter 32 for exposure and a half mirror 33 disposed on theoptical axis of laser beams L1 from the laser light source 31.

The exposure shutter 32 is closed when the recording medium 1 forhologram is not exposed and is opened when the recording medium 1 forhologram is exposed. In addition, the half mirror 33 serves to separatelaser beams L2 passed through the exposure shutter 32 into referencelight and object light. Light L4 reflected by the half mirror 33 servesas reference light and light L3 transmitted through the half mirror 33serves as object light.

On the optical axis of light L4 reflected by the half mirror 33, as theoptical system for reference light, there are arranged a cylindricallens 40, a collimator lens 41 for changing reference light into parallellight, a total reflection mirror 42 for reflecting light configured tobe parallel light by the collimator lens 41 in order recited.

The light reflected by the half mirror 33 is then first configured to bedivergent light by the cylindrical lens 40 and is then configured to beparallel light by the collimator lens 41. Thereafter, such parallellight is reflected by the total reflection mirror 42 and is incident onthe recording medium 1 for hologram.

On the other hand, on the optical axis of light L3 transmitted throughthe half mirror 33, as shown in FIGS. 8A and 8B, as the optical systemfor object light, there are disposed a total reflection mirror 34 forreflecting transmitted light from the half mirror 33, a spatial filter35 in which convex lens and pin hole are combined, a collimator lens 36for allowing object light to be in parallel, a display section 37 fordisplaying picture image to be recorded, and a cylindrical lens 38 forconverging object light onto the recording medium 1 for hologram inorder recited.

Thus, light L3 transmitted through the half mirror 33 is reflected bythe total reflection mirror 34, and is then allowed to be diffused lightfrom spot light source by the special filter 35. Then, such diffusedlight is configured to be parallel light by the collimator lens 36 andis then incident on the display section 37. In this example, the displaysection 37 is e.g., a picture display section of the transmission typecomprised of liquid crystal panel, and serves to display picture imagebased on picture data. D4 sent from the control computer 22.Furthermore, light transmitted through the display section 37 ismodulated in accordance with picture image displayed on the displaysection 37, and is then incident on the cylindrical lens 39.

In addition, light transmitted through the display section 37 isconverged in lateral direction by the cylindrical lens 39, and thisconvergent light is incident on the recording medium 1 for hologram asobject light. Namely, in this exposure processing unit 23, projectedlight from the display section 37 is incident upon the recording medium1 for hologram as strip-shaped rays of object light.

In this case, with respect to reference light and object light,reference light is configured to be incident on one principal surface ofthe recording medium 1 for hologram and object light is configured to beincident on the other principal surface of the recording medium 1 forhologram. Namely, reference light is configured to be incident at apredetermined incident angle on one principal surface of the recordingmedium 1 for hologram, and object light is configured to be incident onthe other principal surface of the recording medium 1 for hologram insuch a manner that the optical axis is substantially perpendicular tothe recording medium 1 for hologram. Thus, the reference light and theobject light interfere with each other on the recording medium 1 forhologram. As a result, interference patterns taking place by suchinterference are recorded onto the recording medium 1 for hologram aschanges of refractive index.

Moreover, this exposure processing unit 23 comprises printer-headportion 43 which can intermittently feed the recording medium 1 forhologram under control of the control computer 22. This exposureprocessing unit 23 carries out intermittent feed of the recording medium1 for hologram by one element hologram on the basis of control signalfrom the control computer 22 every time one picture image is recorded asone element hologram with respect to the recording medium 1 for hologramwhich has been set in a predetermined state at the printer head portion43. Thus, picture images based on picture data processed at the dataprocessing unit 21 are recorded in succession onto the recording medium1 for hologram as element hologram in a manner such that they aresuccessive in the lateral direction.

This exposure processing unit 23 displays, on the display section 37,picture image for exposure based on picture data. Furthermore, theshutter 32 for exposure is opened by a predetermined time so that therecording medium 1 for hologram is exposed.

At this time, light L4 which has been reflected by half mirror 33 oflaser beams L2 emitted from laser light source 31 and transmittedthrough the shutter 32 for exposure is incident on the recording medium1 for hologram as reference light. In addition, light L3 which has beentransmitted through the half mirror 33 results in projected light inwhich picture image displayed on the display section 37 is projected,and such projected light is incident on the recording medium 1 forhologram as object light. Thus, picture image for exposure displayed onthe display section 37 is recorded as strip-shaped element picture ontothe recording medium 1 for hologram.

Furthermore, when recording of one picture image onto the recordingmedium 1 for hologram is completed, the recording medium 1 for hologramis then fed by one element hologram by the printer head portion 43.

The above-mentioned operations are repeated in the state where pictureimages for exposure configured to be displayed on the display section 37are changed in succession in order of parallax picture train. Thus,picture images for exposure based on the original picture data arerecorded in succession as strip-shaped element picture onto therecording medium 1 for hologram.

The printer head portion 43 will be described in detail with referenceto FIG. 9. This printer head portion 43 is adapted so that there aredisposed in succession a film cartridge 71, rollers 70, 72 forintermittent feeding, an optical part 76, a pinch roller 73, anultraviolet lamp 77, a heat roller 78, a pair of feed rollers 79A, 79Bfor feed ejection, and a cutter 80.

This printer head portion 43 is adapted to rotatably axially support,with a predetermined torque, intermittent feeding roller, 70 within thefilm cartridge 71 loaded at a predetermined position, and can hold therecording medium 1 for hologram drawn out from the film cartridge 71 insuch a manner that it is put between the intermittent feeding rollers70, 72 and the pinch roller 73. Thus, the recording medium 1 forhologram is held in a manner substantially perpendicular to the objectlight between the intermittent feeding roller 70 and the intermittentfeeding roller 72.

The intermittent feeding roller 70 and the intermittent feeding roller72 are biased in directions away from each other by torsion coil spring(not shown). Thus, a predetermined tension is applied to the recordingmedium 1 for hologram disposed in such a manner to bridge across theintermittent feeding roller 70 and the intermittent feeding roller 72.As a result, position of the recording medium 1 for hologram isstabilized and vibration is suppressed. It is to be noted that such atension may be applied by the pinch roller system or sprocket feedsystem, etc.

The optical part 76 is adapted so that one-dimensional diffusion plate74 and a louver film 75 are integrally stuck in the state where they arecurved, and is disposed coincided with incident position of object lightbetween the intermittent feeding roller 70 and the intermittent feedingroller 72. This optical part is movably held in a direction close to therecording film 1 for hologram or away therefrom as indicated by arrow bby optical part drive mechanism (not shown).

In this example, the one-dimensional diffusion plate 74 serves to allowholographic stereogram to have angle of visibility in the longitudinaldirection. Namely, by this one-dimensional diffusion plate 74, objectlight is diffused in the longitudinal direction, i.e., in the long axisdirection of element hologram to be made or prepared. Thus, holographicstereogram to be made or prepared has angle of visibility in thelongitudinal direction.

In addition, the louver film 75 is an optical part having fine reedscreen-shaped lattice, and serves to prevent that reference lighttransmitted through the recording medium 1 for hologram is reflected bythe one-dimensional diffusion plate 74 and is incident on the recordingmedium 1 for hologram for a second time.

The printer head portion 43 is driven on the basis of control signaldelivered from the control computer 22 before exposure operation isstarted to move the optical part 76 in a direction close to therecording medium 1 for hologram. Thus, the optical part 76 is pressedonto the recording medium 1 for hologram loaded between the intermittentfeeding roller 70 and the intermittent feeding roller 72. By pressingthe optical part 76 onto the recording medium 1 for hologram in thisway, it is possible to suppress very small vibration of the recordingmedium 1 for hologram. By suppressing very small vibration of therecording medium 1 for hologram as stated above, it becomes possible tomake (prepare) holographic stereogram excellent in the diffractionefficiency and in which bright reproduction image can be obtained.

The intermittent feeding rollers 70, 72 are adapted so that they can bedesirably rotated in the direction as indicated by arrow c by steppingmotor (not shown). This stepping motor rotates intermittent feedingrollers 70, 72 every completion of exposure corresponding to one pictureimage on the basis of control signal S2 delivered from the controlcomputer 22 so that the recording medium 1 for hologram is sent by oneelement hologram every completion of exposure corresponding to onepicture image.

The ultraviolet lamp 77 serves to irradiate ultraviolet rays Lb to therecording medium 1 for hologram sent by the intermittent feeding roller72. As the result of the fact that ultraviolet rays are irradiated ontothe recording medium 1 for hologram by this ultraviolet lamp 77,polymerization of monomer M of the hologram recording layer 3 of therecording medium 1 for hologram is completed.

The heat roller 78 is provided with heating means such as heater, etc.therewithin, and is adapted so that the peripheral surface of the heatroller 78 can maintain temperature of about 120° C. Furthermore, thisheat roller heats the recording medium 1 for hologram to therebyincrease refractive index modulation degree of the hologram recordinglayer 3 to fix recording picture image of the hologram recording layer3.

Ejecting feeding rollers 79A, 79B at the succeeding stage of the heatroller 78 are rotated in a manner synchronous with intermittent feedingroller 72 by drive mechanism (not shown) supplied with control signalfrom the control computer 22. Thus, the protective layer 4 can besecurely held in the state tightly in contact with the peripheral sidesurface of the heat roller 78 without allowing the recording medium 1for hologram to be loosened between the intermittent feeding roller 72and the ejecting feeding rollers 79A, 79B.

Moreover, drive mechanism (not shown) for the cutter 80 drives thecutter 80 at the stage where all area portions in which picture image ofthe recording medium 1 for hologram 1 is recorded are ejected toward theexternal with respect to the cutter 80 after respective picture imagesbased on respective picture data of parallax picture train are recordedonto the recording medium 1 for hologram on the basis of control signaldelivered from the control computer 22 to thereby separate such portionsfrom other portions. Thus, portions where respective picture data ofparallax picture train are recorded of the recording medium 1 forhologram can be ejected toward the external as one holographicstereogram.

In recording three-dimensional picture image onto the recording medium 1for hologram by the printer head portion 43 as described above, controlsignal is first sent out from the control computer 22 to the opticalpart drive mechanism of the printer head portion 43 in the state wherethe recording medium 1 for hologram is loaded across the intermittentfeeding roller 70 and the intermittent feeding roller 72 to drive theoptical part drive mechanism to press the optical part 76 onto therecording medium 1 for hologram at a predetermined pressure.

Then, picture data D4 is sent out from the control computer 22 to thedisplay section 37 of the exposure processing unit 23 to allow thedisplay section 37 to display picture image for exposure based on thispicture data D4, and to send out control signal S1 from the controlcomputer 22 to the shutter 32 to open the shutter 32 by a predeterminedtime to expose the recording medium 1 for hologram.

At this time, light L4 which has been reflected by half mirror 33 oflaser beams emitted from the laser light source 31 and transmittedthrough the shutter 32 is incident on the recording medium 1 forhologram as reference light. Furthermore, light L3 which has beentransmitted through the half mirror 33 results in projected light inwhich picture image displayed on the display section 37 is projected,and this projected light is incident on the recording medium 1 forhologram as object light. In this way, picture image for exposureconfigured to be displayed on the display section 37 is recorded ontothe recording medium 1 for hologram as rectangular element hologram.

Furthermore, after recording of one picture image onto the recordingmedium for hologram is completed, control signal S2 is then sent outfrom the control computer 22 to the printer head portion 43 to feed therecording medium 1 for hologram by one element hologram.

The above-mentioned operations are repeated in the state where pictureimages for exposure configured to be displayed on the display section 37are changed in succession in order of parallax picture train. Thus,picture images for exposure based on picture data processed by the dataprocessing unit 21 are recorded in succession onto the recording medium1 for hologram as rectangular element hologram.

As described above, in this holographic stereogram preparing apparatus,plural picture images for exposure based on output of the dataprocessing unit 21 are displayed in succession on the display section 37and shutter 32 is opened every respective picture images. Thus,respective picture images are respectively recorded in succession ontothe recording medium 1 for hologram as rectangular element holograms. Atthis time, since the recording medium 1 for hologram is fed by oneelement hologram every one picture image, respective element hologramsare recorded onto the recording medium 1 for hologram as plural elementholograms successive in lateral direction. Thus, holographic stereogramhaving parallax in the lateral direction can be obtained.

Thereafter, ultraviolet rays are irradiated over the entire surface ofthe recording medium 1 for hologram thus exposed by ultraviolet lamp 77at the printer head portion 43. Thus, polymerization of monomer M at thehologram recording layer 3 of the recording medium 1 for hologram iscompleted. Furthermore, at the succeeding stage of this ultraviolet lamp77, the recording medium 1 for hologram is heated by heat roller 78. Asa result, refractive index modulation degree of the hologram recordinglayer 3 is increased, thereby the recording picture image being fixed.

Here, there will be added explanation relating to refractive indexes ofbase and protective layer of the recording medium for hologram in thecase where the optical system shown in FIG. 8, i.e., the optical systemfor allowing reference light to be obliquely incident, which is socalled off-axis hologram optical system is used.

In the above-described second model, there has been given, forsimplification of the model, explanation with respect to the opticalsystem where reference light is incident in a manner perpendicular tothe recording medium for hologram, which is so called on-axis hologramoptical system.

Due to-the difference between the off-axis hologram optical system andthe on-axis hologram optical system, consideration must be taken inconnection with

(1) “refraction of rays of light by difference of refractive index whenreference light is incident from air to base, and change of direction ofrays of light based thereon”,

(2) “Change of transmission distance by thickness of the base based onthe fact that rays of light are perpendicularly transmitted within thebase into transmission distance of actual rays of light based on thefact that rays of light are obliquely transmitted within the base”,

(3) “Refractive index vector within the base changes in dependency upondirection where rays of light are incident on the base by thegeometrical relationship between axis of double refraction of base anddirection in which rays of light are incident on the base”, and thelike.

However, also in all of the above-mentioned (1), (2), (3), by replacingphysical quantity such as propagation direction of rays of light bydifference of optical system, etc. or limiting material property ofoptical material, the previously described model can be applied.

With respect to the item (1), direction of rays of light after they areincident is first determined by the Snell laws (rule ofreflection/refraction) from the state of double refraction whenreference light is incident on the base. Furthermore, since the,direction of rays of light is direction of rays of light transmittedthrough the base, the state of double refraction with respect to thatdirection is replaced by the state of double refraction in thepreviously described model so that the previously described model can beapplied.

With respect to the item (2), since phase change based on the fact thatrays of light are passed through the base is determined in accordancewith transmission distance of actual rays of light based on the-factthat rays of light are obliquely transmitted through the base, it issufficient to replace thickness d^(ref) of the base by actualtransmission distance of rays of light.

With respect to the item (3), as the optical state of the example whereuniaxial optical material is used is illustrated by using refractiveindex elliptical body in the above-mentioned drawing, refractive indexvector of base changes in dependency upon whether rays of light areperpendicularly incident or are obliquely incident. By using theexplanation of the item (1) while paying attention to the relationshipbetween incident angle and refractive index vector to replace the stateof double refraction with respect to direction of rays of light by thestate of double refraction in the previously described model, it ispossible to apply the previously described model.

The relationship between the incident angle and the refractive indexvector will be described in a comparative manner with reference to theabove-mentioned FIGS. 6A, 6B, 6C and FIG. 10.

In FIG. 6A, axial direction Y of double refraction of uniaxial opticalmaterial is configured to be thickness direction of strip-shapedrecording medium 65 for hologram. By doing so, there results the statewhere there is no double refraction with respect to laser beams Lperpendicularly incident on the recording medium 65 for hologram.However, there results the state where there is double refraction withrespect to laser beams L obliquely incident on the recording medium 65for hologram. Accordingly, it is necessary to apply the relationshipbetween direction of linear polarization and direction of the axis alongthe model of the previously described on-axis hologram optical system.

In FIG. 6B, axial direction Y of double refraction of uniaxial opticalmaterial is configured to be a direction of the longer side of recordingmedium 66 for hologram. By doing so, it is easy that the direction oflinear polarization is configured to be the same state as that of theaxial direction of double refraction, or perpendicular state theretowith respect to laser beams L incident on the recording medium 66 forhologram. Here, FIG. 10A shows the state of double refraction in thecase where incident plane of incident laser beams is in parallel to thedirection of the longer side, and FIG. 10B shows the state of doublerefraction in the case where incident plane of incident laser beams isperpendicular to the direction of the longer side. In FIG. 10A, doublerefraction n′ in the case where laser beams L′ are incident at incidentangle θ′ which is perpendicular to the recording medium for hologram anddouble refraction n″ in the case where laser beams L″ are incident atincident angle θ″ which is oblique with respect to the recording mediumfor hologram are different from each other. On the other hand, in FIG.10B, both double refractions are the same.

In FIG. 6C, axial direction Y of double refraction of uniaxial opticalmaterial is configured to be coincided with a direction of the shorterside of the strip-shaped recording medium 67 for hologram. Thereby, itis easy that direction of linear polarization is configured to be thesame as axial direction of double refraction or perpendicular theretowith respect to laser beams L incident on the recording medium 67 forhologram. Here, FIG. 10A shows the state of double refraction in thecase where incident plane of incident laser beams is in parallel to adirection of the shorter side, and FIG. 10B shows the state of doublerefraction in the case where incident plane of incident laser beams isperpendicular to a direction of the shorter side. In FIG. 10A, doublerefraction n′ in the case where laser beams L′ are incident at incidentangle θ′ which is perpendicular to the recording medium for hologram anddouble refraction n″ in the case where laser beams L″ are incident atincident angle θ″ which is oblique with respect to the recording mediumfor hologram are different from each other. On the other hand, in FIG.10B; both double refractions are the same.

From the above result, such an approach is employed to use uniaxialoptical material as optical material constituting the recording mediumfor hologram with respect to geometrical shape of strip-shaped recordingmedium for hologram having the longer side-and the shorter side, etc.,and to allow axial direction of that double refraction to be coincidedwith the longer side or the shorter side, thereby making it possible tounivocally determine polarization state of the hologram recording unitalso in the off-axis hologram optical system where laser beams areobliquely incident on the recording medium for hologram. Accordingly,unification and standardization can be made in both hologram recordingunit and recording medium for hologram. Thus, mass production can becarried out and reduction in cost can be realized.

While the example where reference light is passed/emitted through thebase and is incident on the hologram recording layer, and object lightis passed/emitted through the protective layer and is incident on thehologram recording layer has been explained, it is needless to say thatthere may be made change into the example where reference light andobject light are exchanged, and object light is passed/emitted throughthe base and is incident on the hologram layer, and reference light ispassed/emitted through the protective layer and is incident on thehologram recording layer.

In addition, while explanation has been given in connection with therecording medium for hologram consisting of three layers of the base,the hologram recording layer and the protective layer, there may beemployed recording media for hologram consisting of five and sevenlayers of base, hologram recording layer, intermediate layer andprotective layer, etc. as shown in FIGS. 11 and 12, respectively. Alsoin this case, it is desirable that the relationship of doublerefraction, polarization and geometrical shape of the intermediate layeris configured to be the same as the relationship of double refraction,polarization and-geometrical shape of the above-described base andprotective layer.

Explanation will be given in connection with other two more practicalexamples of recording media for-hologram with reference to FIGS. 11 and12. First, recording medium 5 for hologram shown in FIG. 11 is arecording medium of five layers obtained by forming a first hologramrecording layer 7 consisting of photo-polymer layer on a base 6 to forma second hologram recording layer 9 through an intermediate layer 8consisting of colorless and transparent resin film layer thereon tofurther form a protective layer 10 thereon.

Also in this recording medium 5 for hologram, it is similarly desirableto employ material called non-double refraction optical polymer asdescribed above as the base 6, the intermediate layer 8 and theprotective layer 10. Furthermore, axial direction of double refractionof materials of the base 6, the intermediate layer 8 and the protectivelayer 10 is configured to be coincided with the geometrical shape of thephoto-polymer film used as the hologram recording layers in a manner asstated above.

In addition, axial direction of double refraction of materials of thebase 6, the intermediate layer 8 and the protective layer 10 isconfigured to be coincided with polarization of reference light andobject light at the exposure processing unit of the holographicstereogram preparing apparatus.

Thus, also in this recording medium 5 for hologram, it is possible togenerate bright and uniform holographic stereogram without loweringcontrast of interference patterns formed at the hologram recording layercomprised of photo-polymer layer.

Furthermore, a recording medium 11 for hologram shown in FIG. 12 is arecording medium of seven layers obtained by forming a first hologramrecording layer 13 comprised of photo-polymer layer on a base 12 to forma second hologram recording layer 15 through an intermediate layer 14comprised of colorless and transparent resin film layer thereon tofurther form thereon a third hologram recording layer 17 through anintermediate layer 16 thereafter to form a protective layer 18 thereon.

Also in this recording medium 11 for hologram, it is desirable to employmaterial called non-double refraction optical polymer as described aboveas the base 12, the intermediate layers 14 and 16, and the protectivelayer 18.

Furthermore, axial direction of double refraction of materials of thebase 12, the intermediate layers 14 and 16, and the protective layer 18is configured to be coincided with the geometrical shape of thephoto-polymer film used as the hologram recording layers 13, 15 and 17as described above.

Furthermore, axial direction of double refraction of materials of thebase 12, the intermediate layers 14 and 16, and the protective layer 18is configured to be coincided with polarization of reference light andobject light at the exposure processing unit of the holographicstereogram preparing apparatus in a manner as described above.

Also in this recording medium 11 for hologram, it is therefore possibleto generate bright and uniform holographic stereogram without loweringcontrast of interference patterns formed at the hologram recording layercomprised of photo-polymer layer.

It is to be noted that the hologram recording layers of the multi-layerstructure shown in FIGS. 11 and 12 have excellent characteristic withrespect to wavelength of three primary colors of R, G, B and are usedfor generating color holographic stereogram.

Furthermore, while the recording medium for hologram composed of base,hologram recording layer, intermediate layer and protective layer hasbeen described above, there may be provided adhesive layers betweenrespective layers for the purpose of bonding or adhering respectivelayers. At this time, from an optical point of view in the presentinvention, it can be considered that adhesive layers put betweenrespective layers contribute to double refraction in one body as aportion of the base, the intermediate layer or the protective layerrespectively adjacent. Namely, the above-mentioned model can be appliedas layer which provides phase change in one body.

In addition, while explanation has been given by using photo-polymer asphotosensitive material of the hologram recording layer, the presentinvention is not limited to such material. There may be used otherphotosensitive material such as silver salt material or gelatindichromate, etc.

INDUSTRIAL APPLICABILITY

By using the present invention as described above, it is possible torecord bright and uniform hologram without lowering contrast ofinterference patterns formed at the hologram recording layer comprisedof photo-polymer layers.

1. A hologram producing apparatus comprising: a supply unit for arecording medium for hologram, and an exposure unit for irradiatingobject light and reference light onto a recording medium for hologramsupplied from the supply unit to record hologram, wherein the recordingmedium for hologram comprises a hologram recording layer on whichhologram is recorded, and a base and a protective layer between whichthe hologram recording layer is put, and the recording medium forhologram is formed in rectangular shape, the base and the protectivelayer comprise material through which light is transmitted and in whichan axial direction of that double refraction is perpendicular or nearlyperpendicular to the longer side of the rectangular shape and thethickness of the protective layer, the object light and the referencelight that the exposure unit irradiates are linearly polarized lightpolarized in a direction equal or nearly equal to the axial direction ofdouble refraction or in a direction perpendicular or nearlyperpendicular to the axial direction of double refraction.
 2. A methodof preparing a recording medium for hologram comprising a hologramrecording layer in which object light indicating a picture image to berecorded and reference light are irradiated so that hologram isrecorded, and other layer laminated on the hologram recording layer,wherein a shape of the recording medium for hologram is configured to berectangular, and the other layer comprises material through which lightis transmitted, and in which an axial direction of double refraction isperpendicular or nearly perpendicular to the longer side of therectangular shape and the thickness of the other layer, and the objectlight and the reference light are linearly polarized in a directionequal or nearly equal to the axial direction of double refraction or ina direction perpendicular or nearly perpendicular to the axial directionof double refraction.
 3. A hologram producing method of supplying arecording medium for hologram from a supply unit to irradiate objectlight and reference light onto the recording medium for hologram tothereby produce hologram, wherein the recording medium for hologramcomprises a hologram recording layer on which hologram is recorded, andother layer laminated on the hologram recording layer, and is formedinto a rectangular shape and the thickness of the other layer, the otherlayer comprises material through which light is irradiated and in whichan axial direction of double refraction is perpendicular or nearlyperpendicular to the longer side of the rectangular shape, and linearlypolarized light polarized in a direction equal or nearly equal to theaxial direction of double refraction or in a direction perpendicular ornearly perpendicular to the axial direction of double refraction is usedas the object light and the reference light.